In image forming apparatus using electrophotography technology, a higher speed and higher reliability have been pursued severely. Moreover, such image forming apparatus have been started to be used for printing of super fine images such as graphic design and for quick printing required of more reliability (print-on-demand in which a variety of and a small number of prints during work including from editing to copying of a document with a personal computer and bookbinding can be made).
On the other hand, reduction in energy consumption by the apparatus is highly demanded. In order to comply with such a demand, a toner having high low-temperature fixing properties has been strongly needed. However, there is such a problem that if the low-temperature fixing properties are pursued, off-set resistance (anti-offset properties) and blocking resistance (anti-blocking properties) at a high temperature are reduced.
Then, a variety of toners have been proposed in order to satisfy all the low-temperature fixing properties and the off-set resistance and further blocking resistance at a high temperature. A method is proposed in which a binder resin is made to contain two kinds of resins having different softening points as principal components, and to the binder resin, a crystalline polyester having a low melting point is added to improve the low-temperature fixing properties while the off-set resistance and blocking resistance are maintained (see PTL 1). Another method is proposed in which a block polyester including a crystalline block and a non-crystalline block is used as a binder resin to provide a toner having resistance to mechanical stress and sufficient fixing properties (fixing strength) in a wide range of temperature (see PTL 2).
In the methods for producing a toner described in these documents, however, crystallinity of the crystalline component is reduced in a melt kneading step or the like. For this reason, the effect of the crystalline component contained is not sufficiently demonstrated. Accordingly, there is still room for improvement from the viewpoint of keeping stable performances in a long-term use.
As described above, even if the resin itself has sufficient crystallinity, when the resin is formed into a toner, its crystallinity may be lost or reduced to a great extent in many cases. It is difficult to keep the crystalline state of crystalline substances at a high level after forming it into a toner.
Moreover, it is essential to improve dispersibility of other raw material in order to stably keep the quality for a long period of time. However, it is difficult to enhance the dispersibility of other raw material while the crystallinity is kept. To keep the crystallinity of the crystalline substance and to keep the dispersibility of other raw material are not sufficiently satisfied at the same time.